1. Field of the Invention
The invention relates to manganese activated peroxygen bleach compositions with improved bleaching performance.
2. The Prior Art
Dry bleaching powders, such as those for cleaning laundry, generally contain inorganic persalts as the active component. These persalts serve as a source of hydrogen peroxide. Normally, persalt bleach activity in aqueous solution is undetectable where temperatures are less than 100.degree. F. and delivery dosages less than 100 ppm active oxygen. The art has recognized, however, that bleaching under mild conditions may be effectuated through the use of activators. In particular, manganese (II) salts have been reported to be exceptionally effective in activating persalts under mild conditions.
Attempts to improve the bleach activity of manganese (II) salts have been reported. U.S. Pat. No. 4,481,129 discloses bleach compositions containing manganese (II) salts in conjunction with carbonate compounds. U.S. Pat. No. 4,478,733 describes bleach compositions containing manganese (II) salts in conjunction with aluminosilicate cation-exchange materials. U.S. Pat. No. 4,488,980 reports a bleach beneficial interaction between a condensed phosphate/alkali metal orthophosphate mixture and manganese (II) salts.
There are, unfortunately, several problems associated with heavy metal salts. Storage instability is particularly acute. These salts accelerate wasteful peroxide decomposition reactions that are non-bleach effective. Under alkaline conditions, as when used with laundry cleaning compositions, metal cations undergo irreversible oxidation and no longer catalyze. Perversely, the peroxide bleaching reaction is most effective at high pH.
In European Pat. No. 0 072 166, it was proposed to pre-complex catalytic heavy metal cations with a sequestrant and dry-mix the resultant product, in particulate form, with the remainder of the peroxygen containing detergent composition. Storage stability was found to be thereby improved. The patent notes that the complex of catalytic heavy metal cation and sequestrant can be agglomerated in a matrix of pyrophosphates, orthophosphates, acid orthophosphates and triphosphates.
Another problem with manganese (II) cations occurs when they are utilized for whitening laundry. Strong oxidants, such as hypochlorites, are frequently included in laundry washes. Manganese ions will react with these strong oxidants to form manganese dioxide. This compound is highly staining toward fabrics.
Stain problems resulting from free manganese ions have been reduced by binding the heavy metal ion to a water-insoluble support. Thus, European Patent Application No. 0 025 608 reveals a peroxide decomposition catalyst consisting of zeolites or silicates whose cations have been exchanged for heavy metals such as manganese. Co-pending U.S. application Ser. No. 597,971, now U.S. Pat. No. 4,536,183 discloses an activator comprising a water-soluble manganese (II) salt adsorbed onto a solid inorganic silicon support material, the combination having been prepared at a pH from 7.0 to 11.1.
While the foregoing systems provide adequate bleaching and improved stain prevention, there still remain several other problem areas. The prior art catalyst particles are generally in the form of fine powders. When blended with detergent granules, the catalyst powders are easily segregated falling to the bottom of the detergent package. A co-pending U.S. application Ser. No. 805,530 reports solving the foregoing problem by forming aggregated granules prepared by agglomerating, with a binder, a catalyst combination of manganese (II) cation adsorbed onto an aluminosilicate support material. The resultant particles have diameters ranging from at least 250 to 2000 microns. Co-pending U.S. application Ser. No. 668,536 provides a somewhat analogous solution by binding manganese (II) cations to a "ligand" such as zeolite to form a complex. This complex is then protectively enclosed in a matrix of water-soluble or water-displaceable materials. Examples of suitable matrices include modified starch, polyvinyl pyrrolidone, polyvinyl alcohol, sodium carboxymethyl cellulose and glassy phosphates.
Even with all the above-noted advances, non of the art has provided a catalyst system meeting all criteria including those of non-staining, storage stability and commercially acceptable bleach activity.
Accordingly, it is an object of the present invention to provide a bleach formulation based on manganese catalysis of peroxygen compounds that is non-staining and provides improved package storage stability while rapidly releasing active manganese/aluminosilicate particles upon dispersion in water.
Another object of this invention is to provide a manganese catalyst in aggregate form that exhibits enhanced bleaching performance. A further object of this invention is to provide an improved method for bleaching substrates, especially fabrics.